The present invention relates to an air filter that includes a structural component made of a material with anti-microbial properties. More particularly, the invention relates to an air intake filter for a cell culture incubator that includes a structural component that inhibits the reproduction of microbial contaminants and traps them away from the chamber of the incubator.
The use of cell cultures is a tremendously popular research tool in a variety of scientific disciplines. It involves the in vitro growth of cells in a cell culture incubator, for example a humidified CO.sub.2 incubator. The popularity of the technique has lead to many advances in cell growth techniques and equipment, which have made the growth of cell cultures more reliable and reproducible. However, some problems associated with cell culture exist despite the many recent advances made in the field. One of the most prevalent of these problems is contamination.
Many sources exist for the contamination of cell cultures. For example, any piece of equipment that a cell culture may encounter, such as an autoclave, fume hood or incubator, may introduce contaminants into the culture. Humidified CO.sub.2 cell culture incubators are designed to provide a suitable environment for the growth of cells in culture. The primary functional components of these incubators include a chamber in which the cultures are placed for growth, a blower to circulate air in the chamber, a heating system to heat the chamber to an optimal cell growth temperature, and a filter to remove particulate contaminants from the chamber. Additionally, some incubators may include a water pan in the bottom of the chamber to humidify the cell growth environment or a CO.sub.2 input system to vary the makeup of the atmosphere inside the incubator. The resulting warm, moist and dark environment is perfect for the growth of cell cultures. It is also perfect for the growth of bacteria, mold, yeast and fungi contaminants.
Contamination can cause several types of problems in a cell culture incubator. For example, if contaminants infect a cell culture, it may ruin the culture and any experiment relying on that culture. Also, contaminants may grow in the humidity pan. The relative humidity inside an incubator is a function of the evaporation rate of water from the humidity pan. The rate of evaporation is dependent upon the surface area of the pan and the surface tension of the liquid in the pan. If contaminants grow in the pan, they can alter the surface tension of the water and upset the humidity characteristics of the chamber.
To prevent the contamination of a cell culture incubator, the incubator must be cleaned at regular intervals using a rigorous procedure. Even with regular cleaning, however, some locations in the incubator are particularly susceptible to contamination. One of these is the air filter. The air filter in an incubator is generally mounted on an interior surface of the chamber. The blower draws air through the filter, where the air is cleaned of particulate contaminants. Upon leaving the filter, the air flows through a conduit back into the incubator chamber, and is again cycled through the filter. One source of the contaminants removed by the filter is the opening of the chamber door by laboratory personnel. Microbial contaminants, such as bacteria and spores, enter the incubator chamber with each opening of the door. These contaminants are then drawn into the filter by the circulating air and trapped. They may then grow in the filter. Once the filter is contaminated, the potential exists for samples in the chamber to be contaminated as well.
Antibiotics may be added to cell cultures to prevent the contamination of a sample by a contaminated incubator, but they are generally not recommended for use in samples, with limited exceptions. Most antibiotics do not kill the bacteria, but only slow its growth, and thus do not remove the contaminant from the chamber. Also, the long-term use of antibiotics may alter the cultures grown in the incubator, resulting in the selective growth of antibiotic-resistant strains of cells over non-resistant strains. Furthermore, the antibiotic may be toxic to the cultured cells as well. For these reasons, it is not desirable to use an antibiotic in the cell culture to control contamination.
Some materials are known to inhibit the growth of bacteria and other microbial contaminants while showing no toxicity toward eukaryotic cells that are commonly cultured in incubators. Copper and some of its salts and oxides are among these materials. Copper compounds have long been used to control such organisms as algae, mollusks, fungi, and bacteria. Copper sulfate, for example, has many uses in agriculture. It finds its primary use in the control of fungal diseases of plants, but is also used against crop storage rots, for the control and prevention of certain animal diseases such as foot rot, and for the correction of copper deficiency in soils and animals. It also has anti-microbial uses outside of agriculture. For instance, it may be added to reservoirs to prevent the development of algae in potable water supplies. Copper sulfate, however, is not the only copper compound with antifungal and antibacterial applications. Other copper compounds, such as cuprous oxide (Cu.sub.2 O) and copper acetate (CuCH.sub.2 COOH), have also been used as fungicides. Despite its heavy use in agriculture and industry, however, neither copper nor most of its compounds commonly used in these applications have ever been shown to be toxic or to cause any occupational diseases.
Incubators have been constructed with copper chambers in the past to take advantage of the anti-microbial properties of copper compounds. For instance, Revco currently manufactures an incubator with a copper bonded interior surface, the Revco ULTIMA incubator, described in their online catalog at the following website:
http://www.revco-sci.com/catalog/incubators/ultima elite.htm.
It is also available through Fisher Scientific (1994 Fischer Scientific Catalog, p. 1109). The bonded copper interior surface is effective to inhibit the growth of many contaminants. However, contaminants that enter the chamber when the door is opened may still grow in areas not protected by the copper surface, such as the blower, the filter or other components. Moreover, if the filter becomes infected, the blower can spread contaminants from the filter to all other parts of the chamber. The possibility thus exists that some of these contaminants which have grown in the filter and not encountered the copper interior surface may infect cultures in the chamber.
Thus, problems exist both in inhibiting the growth of microbial contaminants in the filter of a cell culture incubator, and in segregating and retaining the inhibited contaminants away from the chamber.